Complete 1st stage failure (scubapro MK5)

[Luis H]

I think even 20 in-lbs is marginal. I ran a quick FEA assuming 35 in-lbs, as suggested by the poster above and was getting stresses 2x the yeild value for stainless steel. I tried pushing the root radius up to .020R which helps but the limiting factor is shank below the threads. And that is where these things do seem to fail in the field. A specialty high strength stainless (say nitronic 50?) might be a better choice. Kind of a marginal design.

I just did a basic classic analysis and I came up with relatively high stresses, but not close to twice the yield strength of SS.

At 35 in*lbf I calculated a combined principal stress (torsional shear + tensile) of 18,876psi. Compared to yield strength for 304SS (35,000 psi), it is kind of high IMO for this type of part.

You may notice that in the drawing I requested a quote with 17-4PH stainless steel. The Navy and other marine industries love that SS for its strength and corrosion resistance.

I would think if the stresses due to torque were twice yield we would be seen far more documented failures. In the 70’s I dough many technician used a torque wrench, I know I didn’t.
IMHO, I am thinking that there may be some conservative assumption in your model.
I am just curious, what FEA software are you using?

If you PM me with you email address, I will be glad to send you a PDF copy of my calculations. Actually, I can send you the Mathcad file if you like.



In any case at this moment the only price quote I got for SS reproduction of the part is too high. I am pursuing locating parts from one of the cloning manufacturers.


In the mean time I think I may switch my wife’s D400 to an Aqua Lung Titan first stage (same as the venerable Conshelf with better LP port location for better hose routing).

I normally use a Royal Aqua Master (Phoenix conversion) double hose regulator (same first stage mechanism as the Conshelf). There are no possibilities of a connection failure in this regulator, since there are no connection or LP hoses to fail…well that was before I added an octopus, etc. I always think it is kind of funny how the extra safety equipment will actually decrease the "meantime between failure" (MTBF).

 

[Mr Carcharodon]

IMHO, I am thinking that there may be some conservative assumption in your model.
I am just curious, what FEA software are you using?

The software was COSMOS (by the way how do you post a plot into a reply?). I did use a generic "chromium steel" as the material which assumed 25KSI yield so that part was conservative. Still if you double the strength it is still marginal. 17-4 looks pretty bullet proof though.

Have you actually seen a torque wrench in a dive shop? I do not think I have so that suggests they are not being used universally.

 

[Nemrod]

I have never seen a torque wrench in actual use in a LDS. In fact I have never seen a torque wrench in use outside of the aerospace industry. In fact it takes a little bit of training and understanding of materials to actually use a torque wrench. These guys use the "Good and Tight" torque method. They put a pair of pliers or whatever Harbor Freight junk open end or adjustable spanner from Home TV and honk on whatever nut, bolt, fastener until their eyes bulge out and they here it squeak.

I have watched this happen--over and over--I have seen the plier marks on the "serviced" regulators. I actually am a trained mechainic, Airframe and Powerplant, and I actually work on turbine engines and various other such things and I know the difference between a mechanic and a HACK. All dive shop service techs that I have seen are HACKS with one exception I met last year. I would not let them work on my lawn mower. Besides, I love my LawnBoy (OMC) mower and don't want it brutalized.

N

 

[DA Aquamaster]

All dive shop service techs that I have seen are HACKS with one exception I met last year. I would not let them work on my lawn mower. Besides, I love my LawnBoy (OMC) mower and don't want it brutalized.

Sadly I agree with you for the most part and my lack of success finding a capable regulator tech was the major reason I started doing regulator repair. I almost reached the same conclusion about A&P's after discovering the ailerons were cross connected on a just annualled V35 Bonanza. Thank God for checking for the need to check for free and PROPER movement of the controls being drilled into my head.

The feeling that there is a lack of competent techs is a sentiment that I suspect is widely shared. I am in an uncomfortable position at present as the shop where I used to do my thing has changed owners and the new owner does not feel he needs my services as he feels that he (with no experience) and the old owner (who is a hack who understands how to use a wrench but does not grasp how regulators really work) can handle the service work themselves.

The thing his customers do not agree and I keep getting asked if I could do the repair and service work on their regulators - which is problematic as I do not have access to parts unless I am working for the shop. Many of these customers would rather skip an annual service than have them mess with their regulators.

 

[Nemrod]

The modern plastic fantastics I consider as disposable regulators, use them a few years and toss them in the garbage. If you follow this philosophy then forego the annual service which is not needed anyways for 90% of regulators. A few years of use from a plastic Apexor or Aqua un-Legendary is about the best you could esxpect anyways.

Somethings should be durable and made of metal--regulators are one of those things that should last a lifetime--a human lifetime.

One of the reasons we have gone to a disposable (eco unflriendly) society is that you would have to train and pay technicians to do these repairs. Why train somebody if you can just sell the customer a new plastic regulator every few years?

N

 

[DA Aquamaster]

One of the reasons we have gone to a disposable (eco unflriendly) society is that you would have to train and pay technicians to do these repairs. Why train somebody if you can just sell the customer a new plastic regulator every few years?

The SP sales rep used to give us a lot of crap for ordering so many Mk 5 and Mk 10 annual service kits. He felt that we would be better off selling all those customers new regulators.

He would be better off with the increased sales, but the shop would have lost customers as the rep is essentially an idiot and seems to miss the point that the local customers tend to be quite conservative and bought SP regs in the first place because they wanted something that was well engineered, designed to last, and virtually guarenteed to be supported for as long as they wanted to continue using it. If we pulled the plug on them for service support, they would indeed buy a new regulator, but probably not a Scubapro and very probably not from us (and definitely not from us if they new that MK 5/MK 10 parts were indeed still available). His marketing philosophy, if carried out, would have meant a big sales boost for the Aqualung/Apeks rep.

It is people like that who will kill off Scubapro if they are left unchecked.

 

[sandersondiver]

The SP sales rep used to give us a lot of crap for ordering so many Mk 5 and Mk 10 annual service kits. He felt that we would be better off selling all those customers new regulators.

He would be better off with the increased sales, but the shop would have lost customers as the rep is essentially an idiot and seems to miss the point that the local customers tend to be quite conservative and bought SP regs in the first place because they wanted something that was well engineered, designed to last, and virtually guarenteed to be supported for as long as they wanted to continue using it. If we pulled the plug on them for service support, they would indeed buy a new regulator, but probably not a Scubapro and very probably not from us (and definitely not from us if they new that MK 5/MK 10 parts were indeed still available). His marketing philosophy, if carried out, would have meant a big sales boost for the Aqualung/Apeks rep.

It is people like that who will kill off Scubapro if they are left unchecked.

I know alot of the guys at SP now, and some that aren't with the company anymore,(retirement), and I never was told by them to push buying new regs. In fact, with all of the product knowledge and especially repair clinics we were encouraged to push the warranty and the fact that they still support regulators that haven't been made for decades.
Anyway, that's just my opinion.

 

[DA Aquamaster]

I know alot of the guys at SP now, and some that aren't with the company anymore,(retirement), and I never was told by them to push buying new regs. In fact, with all of the product knowledge and especially repair clinics we were encouraged to push the warranty and the fact that they still support regulators that haven't been made for decades.
Anyway, that's just my opinion.

I agree with you completely that the value of an SP regulator over other comparable models by other manufacturers lies in the warranty and more importabtly in the history of long term support.

That's also why I felt our particular sales rep was such a self serving idiot.

 

[Luis H]

I know alot of the guys at SP now, and some that aren't with the company anymore,(retirement), and I never was told by them to push buying new regs. In fact, with all of the product knowledge and especially repair clinics we were encouraged to push the warranty and the fact that they still support regulators that haven't been made for decades.
Anyway, that's just my opinion.

This has been one of Scubapro strong point for a long time and one of the reasons I have always like their products. But, I am very disappointed that they are only partially supporting the MK-5 and the adjustable second stage.

They are producing service kits (from parts that are basically interchangeable with their newer regulators), but some of the metal part in the first stage should be available as well as the diaphragm cover and exhaust “T” for the 109.

The fact that they are some of Scubapro oldest regulators should be less important than the fact that they are probably one of the most common regulators still in service. I believe the Mk-5/ R109 is one of only two vintage single hose regulators that has a huge following. The other one being the Conshelf.

IMHO and that of many other, the R109 (converted or not to a balanced adjustable) is one of the best second stages ever made. For Scubapro to abandon it, even partially is a total shame. I have even considering re-chroming some of the worst looking 109 I have bought on eBay. I have converted to balanced adjustable my best five R109.

Scubapro has a great name, but I would think that their image would only benefit by advertising that one of their oldest regulators is still one of many divers “all time favorites”. The “all time favorite” status will quickly disappear if they don’t fully support it.


They started to offer me some kind of a replacement deal for one of my MK-5. IMO, they should be offering a replacement to some of the less successful, more recent, short lived regulators and continue to support one of their most successful regulators ever.

IMO, age is less important than a good sound, great performer, simple, and robust design.

 

[Greg Barlow]

The fact that they are some of Scubapro oldest regulators should be less important than the fact that they are probably one of the most common regulators still in service. I believe the Mk-5/ R109 is one of only two vintage single hose regulators that has a huge following. The other one being the Conshelf.

Luis,

The original Voit/Swimaster MR12 regs are able to be "mostly" serviced using modern day parts. In fact, I have even improved many of them by using silicone second stage diaphragms.

Mares HP poppets, first stage diaphragms, second stage O-rings, MR12 III exhaust valves,and MR12 III second stage poppet seats are all usable in the original MR12 regs.

My favorite vintage single hose reg is the Voit Viking I example of the MR12.

Heck, the MR12 even has the distinction of being the first single hose regulator approved for use by the US Navy. As you probably know, the name MR12 stands for Military Regulator 1 hose, 2 stages.

Greg Barlow